C(m,n)演算法

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排列組合：C(m,n)，m為給定數列，n為要從數列m中取元素的數量，GetResult()擷取所有不重複的組合。

 public class MathCombination<T>    {        List<T> list;        int count = 0;        private MathCombination()        {                    }        public MathCombination(List<T> l, int c)        {            list = l;            count = c;        }        public List<List<T>> GetResult()        {            List<List<T>> result = new List<List<T>>();            List<Dictionary<int, T>> list = GetCombination();            foreach (Dictionary<int, T> item in list)            {                result.Add(item.Select(d => d.Value).ToList());            }            return result;        }        private List<Dictionary<int, T>> GetCombination()        {            List<Dictionary<int, T>> result = new List<Dictionary<int, T>>();            List<Dictionary<int, T>> tempList = new List<Dictionary<int, T>>();            Dictionary<int, T> tempDic = new Dictionary<int, T>();            for (int i = 0; i < list.Count; i++)            {                Dictionary<int, T> dic = new Dictionary<int, T>();                dic.Add(i, list[i]);                tempList.Add(dic);                tempDic.Add(i, list[i]);            }            result = tempList;            for (int i = 1; i < count; i++)            {                result = GetCartesian(result, tempDic);            }            return result;        }        private List<Dictionary<int, T>> GetCartesian(List<Dictionary<int, T>> listDic, Dictionary<int, T> dic)        {            List<Dictionary<int, T>> result = new List<Dictionary<int, T>>();            foreach (Dictionary<int, T> d in listDic)            {                foreach (KeyValuePair<int, T> k in dic)                {                    if (!d.ContainsKey(k.Key) && d.Keys.OrderByDescending(o => o).FirstOrDefault() < k.Key)                    {                        Dictionary<int, T> tempDic = new Dictionary<int, T>(d);                        tempDic.Add(k.Key, k.Value);                        result.Add(tempDic);                    }                }            }            return result;        }    }

調用：

            List<decimal> listOdd = new List<decimal>() { 1.0M, 2.0M, 3.0M, 4.0M };            MathCombination<decimal> m = new MathCombination<decimal>(listOdd, 4);            List<List<decimal>> list = m.GetResult();